Here's why:
* "However" is an adverb that introduces a contrasting idea. It acts as a conjunction, similar to "but" or "yet".
* Commas are used to separate independent clauses connected by conjunctions.
Example:
* Incorrect: I wanted to go to the party, however I was too tired.
* Correct: I wanted to go to the party, however, I was too tired.
Important Note: When "however" starts a sentence, it is followed by a comma.